Green approaches to catalytic epoxidation of olefins

Abstract

Epoxides are useful intermediates for the synthesis of a range of chemicals with a variety of commercial applications. Epoxidation of olefins is an important reaction in organic chemistry. Many studies have shown that high yield and selectivity of epoxide can be obtained efficiently by different catalyzed reaction systems. Nevertheless, most of the reported studies needed to use organic solvents and/or toxic catalyst. The work presented in this thesis aims to develop some simple, inexpensive, environmentally friendly and scalable methods for olefin epoxidation Chapter 2 shows a chemoenzymatic approach for the in situ generation of hydrogen peroxide in the epoxidation of olefins. In this system, hydrogen peroxide can be simply produced by enzymatic oxidation of glucose in aqueous medium. Water-soluble olefins were oxidized with oxygen/glucose/glucose oxidase and Mn11/HCO3- to afford excellent yields of epoxides. By using sodium dodecylsulfate (SDS), lipophilic olefins could be effectively epoxidized with similar conditions without the need for an organic co-solvent. The use of immobilized GOx was explored and it was found that chemically immobilized GOx on silica gel was stable and could be reused up to ten cycles. Ionic liquids are considered as "green" or "clean" solvents as they are non-volatile and potentially easily recycled. In Chapter 3, a simple catalytic system, manganese sulfate/bicarbonate, was developed to epoxidize olefins with hydrogen peroxide in the room temperature ionic liquid, 1-butyl-3-methylimidazolium. The ionic liquid itself can be easily recovered and re-used. Epoxidation of terminal olefins remains a challenging task in organic chemistry. In Chapter 4, a useful method for the epoxidation of unactivated olefins using a modified bis-phenanthroline iron dimer as catalyst in ionic liquids as the reaction medium was developed. By using this catalytic system, a wide range of terminal olefins could be simply oxidized to epoxides by peracetic acid in minutes. The ionic liquid could be easily recycled and re-used. The mechanism of the reaction was discussed.